This invention relates to an axial flow thresher, usable, for example, in an axial flow combine harvester, and particularly to a grate clearance adjusting arrangement for such a thresher.
In one already known arrangement (see, for example, U.S. Pat. No. 3,589,111 Gullickson), the threshing grate, surrounding a rotor threshing portion, is formed in two halves pivoted together along a center line underneath the rotor. An adjusting device varies the separation between the top longitudinal edges of the grate halves. With such an arrangement, in which the gap or radial clearance remains fixed at the location of the pivot axis, the gap tapers, more or less, around the periphery over the adjustment range.
In another known arrangement (see, for example, U.S. Pat. No. 2,053,148 James), the grate consists of two diametrically opposed halves, each movable towards and away from the rotor axis so as to vary grate-to-rotor clearance. Clearly, when the radius of curvature of the grate halves is fixed, there will be a tapering clearance between each grate and rotor except when the grate is in a setting concentric with the rotor.
Both the above and other known adjustment arrangements result in configurations of grate to rotor clearance adverse to good threshing function.